diy solar

diy solar

This is my schematic. Is it correct?

MikeMynis

MikeMynis

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Apr 21, 2022
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Hi, I just found this awesome forum, where I can finally ask questions. I'm pretty new in DIY solar, however, I do have tech background.

After searching and doing some research, I created a schematic for an off grid solar system. Can some of you please take a look at it and tell me if I'm on the right track?

It's 9 panels connected in series to create high voltage/lower current input power to a Growatt SPF 5000ES, which support solar input voltage of up to 430 Volts.
The Growatt is connected to 2 lead acid battery banks. Each bank (or array) has four 12 Volt batteries, making 48 volts. Each battery is 260Ah.
There are 3 battery balancers placed to create equal charging loads on the batteries.
Then there is a shunt, but I don't know which one to use, and a BMV702 to know the status of the system.

The rest of the schematic speaks for itself.

Can I build it like this? What do you think?
Are there things missing or incorrectly placed/used?

Please let me know...

Thanks!

schematic solar 1.jpg
 
@MisterSandals, aha. Good point. I've looked it up. The Voc is indeed 49.30 V.
9 x 49.30 = 443,7 Volt, which is higher than the max input voltage of the SPF 5000.
So I guess your gut feeling is correct...

Coldest temps is around 8 degrees celsius. (night time in the winter in southern Spain.)
Panel temp coefficients sre these:

Coeficient Temp. de Isc (TK Isc) 0.049 % /°C
Coeficient Temp. de Voc (TK Voc) -0.271 % /°C
Coeficiente Temp. de Pmax (TK Pmax) -0.352 % /°C
 
MisterSandals said:
You need temp compensation too in the equation.
Click to expand...
Okay, how do I calculate that based on these coefficients?

Coeficient Temp. de Isc (TK Isc) 0.049 % /°C
Coeficient Temp. de Voc (TK Voc) -0.271 % /°C
Coeficiente Temp. de Pmax (TK Pmax) -0.352 % /°C
 
Specs panel:
1650571804117.png
Vmp = 41.50 V.
8 x 41.5 = 332 V.


SPF 5000 specs:
Screenshot_5.png
MPPT range = 120V - 430V, so it looks like 8 x the Vmp (332 V.) is okay.
 
So, it's going to be 8 panels instead of 9.
How about the number of batteries?

Each battery is 12 Volt / 260Ah. I have 8 of them.

I have two arrays of each 4 batteries (batteries in series).
So, each array is 48 Volt.

Both arrays are parallel connected, resulting in still 48 volts, but double current.

To equalize the load for all batteries, I want to use 3 Victron Battery Balancers.

Is a total of 8 x 260Ah batteries okay?
 
MikeMynis said:
To equalize the load for all batteries, I want to use 3 Victron Battery Balancers.

Is a total of 8 x 260Ah batteries okay?
Click to expand...
I do not have experience with a big lead 48V bank. Hopefully you have sized everything based on an energy audit.

I am not sure you will need the balancers but Victron makes great stuff.
 
Well, it's based on a very basic energy audit. My idea is to build one system, and then see how it performs. Based on the results I can add a second or even third system, making 2 or 3 energy groups. But I wanted to start with this 'smaller' setup. But the thing is that I don't know yet how to calculate the number of batteries I can connect to the Growatt. At least 4, of course, to make 48 Volts. The batteries are 12V/260Ah each. So that makes this array 48V/260Ah. Can the Growatt handle this? And maybe I can even connect a second array of 4 batteries, parallel to the first one, making 48V/520Ah.

Not sure how to calculate what fits the Growatt.
 
MikeMynis said:
The batteries are 12V/260Ah each. So that makes this array 48V/260Ah. Can the Growatt handle this? And maybe I can even connect a second array of 4 batteries, parallel to the first one, making 48V/520Ah.
Click to expand...
The Growatt does not need to know and does not care how big the battery is in terms of Ah. Its kind of like asking how big of a gas tank an engine can handle.

Yes, multiple 48V batteries in parallel to make a larger battery bank is the way to increase capacity.
 
However, this is true when the Growatt only uses power from the batteries. But the Growatt also charges these batteries.
So it sends power to the batteries, and I see in the Growatt specs above that the maximum solar charge current is 100A.

Is 100A enough to charge 1 or 2 (parallel) of these battery arrays?
 
MikeMynis said:
Is 100A enough to charge 1 or 2 (parallel) of these battery arrays?
Click to expand...
To stick with the gas tank capacity example, is one gallon per hour fast enough to fill a 50 gallon tank. Yes, it will eventually fill it every time at that rate. Its all a matter of the and whether you are using power at the same time.

How much time do you need to 100% charge your 48V/520Ah battery bank with 8x 450W?
Assuming your 12V batteries ar 12.8V nominal so 48V is 51.2V
51.2V x 520Ah = 26,624Wh (lead acid is 50% usable so half if this) 13,312Wh lead acid

Your array 8 x 450W = 3600W

13,312Wh / 3600W = 3.7h to charge with everything operating at 100% (and no loads)

100A charging at 56V = 5600W
Your array can only provide 3600/5600= 64% of what the Growatt is rated for.
 
Ah, thanks again so much for the calculation. :)

So basically 2 arrays (8 batteries) is not 'too much' for the Growatt. I like gas tank example, haha.

I could even add a 3rd array, making it 12 x 450W = 5400W, which is a lot closer to the 5600W (96%), right?
 
MikeMynis said:
I could even add a 3rd array, making it 12 x 450W = 5400W, which is a lot closer to the 5600W (96%), right?
Click to expand...
You are confusing me with your use of array for panels and batteries. I thought you have 2x 48V batteries in parallel making a 520Ah bank.

You have 1 solar array of 8 panels in series. How do you get to adding a 3rd (solar?) array? What was the second array?
 
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